The prior art is replete with disclosures directed at converting starch or related materials into a molded or shaped article. The following discussion therefore provides a brief chronological overview of the development of such technology as it has appeared in the patent literature over the past several decades.
For example, starting with U.S. Pat. No. 2,602,755 (1952) entitled "Thermoplastic Compositions of Water-Soluble Cellulose Ethers" it was disclosed that powdered methyl cellulose of a water soluble variety could be blended with a particular narrow range of mixtures of propylene glycol and glycerin to provide compositions which could be molded or extruded when pressure was applied at temperatures of 150.degree. to 170.degree. C., without decomposition. This was then followed by U.S. Pat. No. 3,137,592 (1961) entitled "Gelatinized Starch Products" which described a method of preparing homogenous gelatinized starch products, which method was characterized by intense mechanical working or shearing of the starch at elevated temperatures and pressures in the presence of a minor-proportion of a starch-swelling agent. The method goes on to disclose the use of a screw-type extruder, along with water as the preferred starch-swelling agent or plasticizer due to its low cost and relatively low boiling point.
Attention is next directed to U.S. Pat. No. 3,038,895 (1962) entitled "Water-Dispersible Partially Substituted Derivatives of Amylose" which describes a means for producing an amylose derivative which was readily dispersed in water without the need to exceed temperatures above 130.degree. C., which dispersion was identified as "viscosity stable", thereby forming films of excellent water resistance. Shortly thereafter, in U.S. Pat. No. 3,074,803 (1963) entitled "Molding Starch Composition" a method was disclosed for preparing molded starch compositions, which method focused on the blending of high melting point fatty acid esters with starch which blends are then said to provide a composition relatively free of oil build-up along with what was said to be a minimum of starch dusting.
This was followed by U.S. Pat. No. 3,117,014 (1964) entitled "Amlaceous Compositions for Shaped Articles and Process" which described starch compositions which are said to flow under heat and pressure which compositions comprise a derivative of amylaceous material, a plasticizer for said derivative, and water, wherein the amount of water is between 1.0-20% by weight. Turning next to U.S. Pat. No. 4,076,846 (1978) entitled "Protein-Starch Binary Molding Composition and Shaped Articles Obtained Therefor" an edible, water-soluble thermoplastic molding composition comprising a starch material is disclosed, along with a neutral inorganic alkali salt of protein material, water, an edible plasticizer, an edible lubricant, and other additives. Such compositions were said to have excellent moldability and processibility when subjected to various common plastics processing techniques, such as compression molding, transfer molding, extrusion molding, blow molding, inflation molding, injection molding, vacuum forming, pressuring forming, heat sealing, etc.
More recent disclosures include U.S. Pat. No. 4,673,438 (1987) entitled "Polymer Compositions and Injection Molding". This disclosure states that capsules and other shaped products can be formed from a starch composition comprising starch, with a molecular mass range of 10,000 to 20,000,000 Daltons, along with a water content from 5-30% by weight. The recited process using an injection molding machine requires that one maintain a starch/water composition at a water content of 5-30% by weight of the composition under controlled conditions of temperature and pressure, heating said starch/water composition at elevated pressure above its glass transition temperature and melting point while maintaining said water content to form a melt, further heating and plasticizing said molten starch/water composition to dissolve the starch in the water to form what is stated to be an essentially molecularly dispersed solution of the melt. This is followed by injecting the starch/water melt into a mold cavity while maintaining a predetermined water content, and cooling the composition in the mold to form a molded product at a temperature below the glass transition temperature of the composition and ejecting the molded product from the mold.
In U.S. Pat. No. 4,738,724 (1988) entitled "Method for Forming Pharmaceutical Capsules from Starch Compositions" injection molded capsules of starch are disclosed, for pharmaceutical applications, which method, similar to the '438 Patent discussed above, recites that one first provide a starch water mixture having a water content in the range of about 5 to 30% by weight based on the weight of starch and water. This is followed by heating the starch/water composition at elevated temperatures above its glass transition temperature and melting point while maintaining the water content to form a melt, followed by further heating and plasticizing said molten starch-water composition to dissolve the starch in the water followed by injection molding of the plasticized starch at elevated temperature and pressure into a mold, and forming a multi-chambered configuration, and ejecting the molded capsule from the mold.
U.S. Pat. No. 5,405,564 (1995) entitled "Method of Forming Shaped Articles Made From Pre-Processed Starch" recites a process of forming shaped articles from starch. The method is described as having surprisingly established that in the process of injection molding starch, there are two important steps that are preferably separated. That is, this disclosure recites that one must first heat a starch/water mixture wherein the water content is about 10% to about 20% by weight with respect to that of said starch, in a closed volume to a temperature within the range of about 120 .degree. C. to about 190 .degree. C. at a pressure corresponding to the vapor pressure of water as the used temperature and up to about 150.times.10.sup.5 N/m.sup.2, to form a melt, wherein said melt is extruded and cooled to a solidified and granulated product. This is then followed by heating such solid starch composition, wherein the water content of said solid composition is about 10% to about 20% by weight with respect to that of said starch, in the screw barrel of an injection molding machine or an extruder, at a temperature of from about 80.degree. C. to about 200.degree. C., and at a pressure of from about zero to about 150.times.10.sup.5 N/m.sup.2 for a time long enough to form what is termed as a melt of destructurized starch, transferring said melt of destructurized starch to a mold or extruding said melt of destructurized starch while maintaining the water content in the range of from about 10% to about 20% by weight with respect to that of the composition, and cooling said melt of destructurized starch in said mold or outside said extruder to form a solid shaped article.
Finally, attention is directed to the following U.S. Patents and copending applications, commonly owned by the assignee herein: U.S. Pat. Nos. 5,200,212; 5,240,720; 5,476,069; U.S. patent application Ser. Nos.: 08/923,070 filed Sep. 3, 1997 entitled "Vegetable Based Dog Chew"; U.S. Pat. Nos. 5,827,565; 5,941,197; U.S. patent application Ser. Nos. 08/888,611 filed Jul. 7, 1997 entitled "Vegetable Dog Chew" now abandoned; 09/114,872 filed Jul. 14, 1998 entitled "Heat Modifiable Edible Dog Chew" now abandoned; U.S. Pat. No. 5,086,940; U.S. patent application Ser. Nos. 09/138,804 filed Aug. 21, 1998 entitled "Improved Edible Dog Chew"; 09/116,070 filed Jul. 15, 1998 entitled "Wheat & Casein Dog Chew With Modifiable Texture"; 09/116,555 filed Jul. 15, 1998 entitled "Heat Modifiable Peanut Dog Chew". In addition to such patents and applications, attention is also directed to the art cited in said patents and applications, as such art relates to the field of molded starch products.
As is apparent from the above review of the prior art, a variety of efforts have been developed to convert starch, with minimum degradation, into a molded product of a desired configuration. Such efforts have focused on the use of propylene glycol, fatty acid esters, alkali salts of protein material and/or water as a starch additive, followed by melt processing techniques such as extrusion and/or injection molding. With respect to the use of water, although it has been disclosed that water apparently assists in regulating starch degradation, there has been an intensive and on-going search for some key or optimum water level, which when combined with a corresponding optimum processing profile, fully prevents the starch from overheating and ultimately degrading, and therefore leading to the development of molded products of highest possible quality.
Accordingly, the present invention has as its primary object to formulate a starch composition, followed by a processing/molding profile, which formulation and processing/molding profile affords a molded starch product with mechanical property performance that vastly improves over those starch products reported in the art.
In addition, it is also a primary object of this invention to develop and optimize the additive level for a starch composition such that the starch, subsequent to a desired melt processing technique and conversion into a desired shape, will have optimum and unique properties suitable for the manufacture of an edible starch product and/or chew toy for a pet.